Retractable compliant abradable sealing system and method for rotary machines

ABSTRACT

An abradable structure is provided on an inner face of a stationary component of the rotary machine or on a rotating component. During operation of the rotary machine, operating fluid pressure biases the stationary component against the rotating component, allowing minimal clearances to be maintained between the rotating component and the stationary component resulting in reduced fluid leakage and increased efficiency of the rotary machine. During start-up, shut down, or other transient conditions of the machine, a retractable mechanism biases the stationary component away from the rotating component ensuring preservation of a plurality of teeth provided on the stationary component or the rotating component.

BACKGROUND

The invention relates generally to a rotary machine and, moreparticularly, a sealing system for an interface between rotating andstationary components. As discussed below, certain embodiments of theinvention include a retractable abradable sealing system for a rotarymachine, and a method of operating a rotary machine for facilitating aminimum dynamic clearance during steady state and transient operatingconditions of the rotary machine.

In rotary machines, one or more seals extend along an interface betweenrotating and stationary components. For example, compressors andturbines may have one or more seals, e.g., labyrinth seals, at theinterface between a series of rotating blades disposed within a casingor vane. These seals are intended to preserve a pressure differentialacross the rotating components, e.g., blades, between upstream anddownstream sides of the rotary machine. A smaller clearance at the sealgenerally increases the performance of the seal. Unfortunately, therotating components, e.g., blades, increase the difficulty in attainingand maintaining a smaller clearance at the seal. In certain rotarymachines, such as gas turbine engines, the seals are subject torelatively high temperatures, thermal gradients, and thermal expansionand contraction of the components during various operational stages. Forexample, the clearance can increase or decrease during variousoperational stages of the rotary machine. Typically, the seal includesextra clearance to reduce the likelihood of contact and damage betweenthe rotating and stationary components. However, the extra clearancealso reduces the efficiency and performance of the rotary machine,because extra leakage occurs across the seal.

Accordingly, there is a need for a technique that reduces leakage offluid in a rotary machine, and that maintains minimum clearance withoutimpairing the performance of a seal during steady state operatingconditions and maintains clearance at all operating points duringtransient operating conditions. In addition, a system for reducingleakage of fluid in a rotary machine during steady state and transientoperating conditions is also desirable.

BRIEF DESCRIPTION

In accordance with one aspect of the present invention, a rotary machinecomprises a first member, and a second member, wherein the first memberis configured to rotate relative to the second member or the secondmember is configured to rotate relative to the first member. Aretractable abradable seal is disposed between the first and secondmembers.

In accordance with another aspect of the present invention, a systemcomprises a retractable abradable seal. The seal comprises a retractablemechanism configured to couple to a second member opposite from a firstmember, wherein the first member or the second member is configured torotate. A first seal portion is disposed on the retractable mechanism. Asecond seal portion is configured to be disposed on the first member andmate with the first seal portion, wherein the first seal portion or thesecond seal portion comprises an abradable structure.

In accordance with another aspect of the present invention, a method ofoperating a rotary machine includes rotating a first member relative toa second member or rotating the second member relative to the firstmember. The method also includes providing a zero-clearance labyrinthseal between the first and the second members via a retractableabradable seal disposed between the first and the second members.

In accordance with another aspect of the present invention, a method ofmanufacturing a rotary machine includes disposing a retractableabradable seal between a first member and a second member. The methodalso includes coupling a retractable mechanism to a second memberopposite from a first member, wherein the first member or the secondmember is configured to rotate. A first seal portion is disposed on theretractable mechanism. A second seal portion is disposed on the firstmember to mate with the first seal portion; wherein the first sealportion or the second seal portion comprises an abradable structure.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical view of a gas turbine engine system having aretractable abradable sealing system in accordance with an exemplaryembodiment of the present invention;

FIG. 2 is a diagrammatical view of a retractable abradable sealingsystem for a rotary machine, e.g., a compressor, in accordance withaspects of FIG. 1;

FIG. 3 is a diagrammatical view of a retractable abradable sealingsystem for a rotary machine, e.g., a compressor, in accordance withaspects of FIG. 1;

FIG. 4 is a cross sectional view of an abradable coating having drilledholes in accordance with aspects of FIG. 2;

FIG. 5 is an axial view of a retractable abradable sealing system for arotary machine, e.g., a compressor, in accordance with an exemplaryembodiment of the present invention;

FIG. 6 is a diagrammatical view of a retractable abradable sealingsystem having a plurality of teeth detachably fitted to a rotatingcomponent of a rotary machine, e.g., a compressor, in accordance with anexemplary embodiment of the present invention;

FIG. 7 is a diagrammatical view of a retractable abradable sealingsystem for a rotary machine, e.g., a compressor, in accordance with anexemplary embodiment of the present invention;

FIG. 8 is a diagrammatical view of a retractable abradable sealingsystem for a rotary machine, e.g., a steam turbine, in accordance withan exemplary embodiment of the present invention;

FIG. 9 is a flow chart illustrating exemplary steps involved in a methodof operating a retractable abradable sealing system in accordance withan exemplary embodiment of the present invention; and

FIG. 10 is flow chart illustrating exemplary steps involved in method ofmanufacturing a retractable abradable sealing system in accordance withan exemplary embodiment of the present invention.

DETAILED DESCRIPTION

As discussed in detail below, embodiments of the present inventionprovide a rotary machine, in which operating fluid pressure opposespressure exerted by a retractable mechanism in the rotary machine. Anabradable structure is provided on an inner face of a stationarycomponent of the rotary machine or on a rotating component. Duringoperation of the rotary machine, operating fluid pressure biases thestationary component against the rotating component, allowing minimalclearances to be maintained between the rotating component and thestationary component resulting in reduced fluid leakage and increasedefficiency of the rotary machine. The rotating component is rotatablerelative to the stationary component to form a plurality of permanentsealing grooves in the stationary component or in the rotating componentdue to interference. During start-up, shut down, or other transientconditions of the machine, the retractable mechanism biases thestationary component away from the rotating component ensuringpreservation of a plurality of teeth provided on the stationarycomponent or the rotating component. The rotary machine, in accordancewith aspects of the present invention, facilitates removal of therotating component from the seal cavity of the machine for maintenance.Specific embodiments of the present invention are discussed belowreferring generally to FIGS. 1-10.

Referring to FIG. 1, an exemplary rotary machine (example, gas turbineengine system) 10 is illustrated in accordance with aspects of thepresent invention. The illustrated machine 10 includes a gas turbineengine 12 having a compressor 14, a turbine 16, and a gas turbine shaft18 coupling the compressor 14 rotatably to the turbine 16. The gasturbine engine 12 also includes one or more combustors 20, such as anannular or can-shaped combustor. The gas turbine engine 12 also may becoupled to a variety of loads 22. Furthermore, the gas turbine engine 12includes a retractable abradable sealing system 24 disposed in thecompressor 14 and/or the turbine 16. The retractable abradable sealingsystem 24 is discussed in further detail below.

The compressor 14 is coupled to the combustor 20 to supply compressedair into the combustor 20. The temperature of the compressed airgenerally increases due to compression. The compressed air mixes with afuel (e.g., natural gas) and combusts inside the combustor 20, therebyproducing hot products of combustion. The turbine 16 extracts energy byexpansion of the hot products of combustion for rotating the gas turbineshaft 18 coupled to the compressor 14. More specifically, an outlet ofthe combustor 20 is coupled to an inlet of the turbine 16 to force thehot products of combustion through one or more sets of blades within theturbine 16. As a result, the hot products of combustion force the bladesand, thus, the shaft 18 to rotate about an axis of the gas turbineengine 12. In turn, the rotating shaft 18 drives the compressor 14,which continues to supply compressed air to the combustor 20. Inaddition, the load 22 may be mechanically coupled to the turbine 16. Thegas turbine engine 12 is operated to maintain the load 22 at a desiredspeed and other characteristics. In other embodiments, the load 22 mayinclude a power generator, a pump, a propeller of an aircraft orwatercraft, an industrial machine, one or more wheels of a land vehicle,and so forth. Of course, the illustrated engine system is merely anexample, as the present invention affords benefits to any number ofsystems in which steam or gas leakage is a concern. In another exemplaryembodiment, the rotary machine may include a centrifugal compressor.

Gas leakage, either out of a gas path, or into the gas path of therotary machine 10 from an area of higher pressure to an area of lowerpressure, is generally undesirable. For example, a gas path leakage inthe turbine 16 and/or compressor 14 of the rotary machine 10 may lowerthe efficiency of the gas turbine leading to increased fuel costs. Inthe illustrated embodiment, the retractable abradable sealing system 24is provided in the compressor 14 and/or the turbine 16. The retractableabradable sealing system 24 facilitates minimum clearance between astationary component and a rotating component in the compressor and/orturbine. As a result, fluid leakage through the rotary machine isminimized and the overall efficiency is enhanced. The retractableabradable sealing system 24 in accordance with aspects of the presentinvention, are explained in greater detail with respect to subsequentfigures.

Referring to FIG. 2, a rotary machine (for example, the rotarycompressor) 14 is illustrated in accordance with certain embodiments ofthe present invention. In the illustrated embodiment the rotarycompressor 14 includes a first member 26 disposed inside a second member28. The first member 26 comprises a rotor and the second member 28comprises a stator or stationary housing. In an alternate embodiment,the first member 26 may include the stator or stationary housing and thesecond member 28 may include the rotor. The first member or rotor 26 iscoupled to an input drive shaft extending lengthwise relative to theillustrated rotor 26, such that the rotor can rotate about an axis 23 asillustrated by rotational arrow 25. The second member or stator housing28 includes a plurality of suction ports and discharge portscommunicating gases to or from the rotor 26. During rotation of therotor 26, fluid is sucked through the suction ports and the compressedfluid is discharged through the discharge ports. The retractableabradable sealing system 24 is provided between the rotor 26 and thestator housing 28 and configured to control the leakage of fluid betweenthe rotor 26 and the stator housing 28. Although in the illustratedembodiment, the rotary compressor is illustrated, in other exemplaryembodiments, the sealing system in accordance with the aspects of thepresent invention may be used in other rotary machines, for example, asteam turbine, a compressor, a gas turbine, or the like.

The sealing system 24 includes a first seal portion 30 disposed in agroove, channel, or slot 32 formed in the stator housing 28. Forexample, the first seal portion 30 may include a retractable sealportion, such as an annular structure (e.g., an I-shaped packing ring),which can move radially inward and outward relative to the rotor 26 asillustrated by arrow 27. Thus, the slot 32 may have a similar annulargeometry, such as an I-shaped annular slot, along the interior of thestator housing 28. During operation, the system can bias the first sealportion or packing ring 30 toward the rotor 26 under certain conditions,while retracting the packing ring 30 away from the rotor 26 into theslot 32 under other conditions. The packing ring 30 includes anabradable structure 34 disposed on a substrate 36. The abradablestructure 34 is configured to enhance the wear resistance of the firstseal portion or packing ring 30. The abradable structure 34 may beapplied by a variety of manufacturing techniques, such as molding,diffusion bonding, brazing, thermal spraying, or combinations thereof.The abradable structure or coating 34 may be adaptable to variousoperating conditions, such as operating temperature of the sealingsystem 24, rotor speed, incursion rate, or the like.

In one embodiment, the abradable structure or coating 34 may include analloy of cobalt, nickel, chromium, aluminum, yttrium, hexagonal boronnitride, and polymers such as polyesters, polyimides, or the like. Inanother embodiment, the abradable structure or coating 34 may includenickel, chromium, aluminum, and clay (bentonite). In yet anotherembodiment, the abradable structure or coating 34 may include nickel,graphite, and stainless steel. In yet another embodiment, the abradablestructure or coating 34 may include nickel, chromium, iron, aluminum,boron and nitrogen. In yet another embodiment, the abradable structureor coating 34 may also include non-metallic materials (e.g.polytetrafluoroethylene applied by electrostatic powder coating processor polytetrafluoroethylene filled synthetic mica which may be attachedby a mechanical device). Similarly, in the other embodiments, othercompositions of the abradable structure or coating 34 are alsoenvisaged.

In one example, the substrate may be composed of carbon steel, althoughother materials may be suitable, depending upon such factors as thedesign of the machine, operating temperatures and transients, the fluidtreated (i.e., compressed), and so forth.

In the illustrated embodiment, a retractable mechanism 37 including aplurality of biasing members 38, such as springs, are disposed betweenthe packing ring 30 and the stator housing 28. Exemplary springs mayinclude leaf springs, coil springs, helical springs, hydraulic springs,pneumatic springs, stacked washers provided in a housing or the like.The springs 38 are configured to bias the packing ring 30 away from asecond seal portion 40 provided on the rotor 26. The packing ring 30 isradially movable with respect to the housing 28. In an alternateembodiment, the retractable mechanism 37 may be provided to the firstmember 26. The arrangement, number, and type of springs may be varieddepending on the application. In another exemplary embodiment, theretractable mechanism 37 includes permanent magnets, or electromagnets.In the illustrated embodiment, the second seal portion 40 includes aplurality of protruding members or teeth 42 formed integrally on therotor 26. The height of the teeth corresponds to the maximum radialincursion of teeth 42 into the abradable coating 34 of the packing ring30. The abradable coating 34 typically protects packing ring 30 againstpossible wear due to interference between the packing ring 30, itself,and the plurality of teeth 42 during typical operating conditions, suchas during start-up, and transient conditions of the rotary compressor14.

Referring to FIG. 3, a rotary machine (for example, the rotarycompressor) 14 is illustrated in accordance with certain embodiments ofthe present invention. During operation of the machine, gas entersthrough the suction ports and exits through the discharge ports of thestator housing 28. The gas pressure exerted on a top side 44 of thepacking ring 30 forces the packing ring 30 against the plurality ofteeth 42 provided on the rotor 26 to maintain a minimal clearancebetween the packing ring 30 and the teeth 42. In this manner, theminimized clearance improves operational efficiency and performance ofthe system. For example, during start up of the rotary compressor, thetip portions of the plurality of teeth 42 slide over the surface of theabradable coating 34 due to the interference between the packing ring 30and the teeth 42. The combined effect of centrifugal forces and theforces resulting from biasing the packing ring 30 against the teeth 42dislodges the particles in the abradable coating 34, causing anincursion of the teeth 42 in the abradable coating 34. As a result, aplurality of permanent sealing grooves 43 may be formed in the abradablecoating 34. In one example, during start-up operation of the rotarycompressor, the sealing grooves have a profile matching as that of theteeth 42. As a result, close clearance is maintained between the sealingelements.

During start-up, shut down, or other conditions in which gas pressure isminimum, the springs 38 bias the packing ring 30 away from the rotorteeth 42 ensuring preservation of the teeth 42. In other words, agreater clearance exists between the coating 34 and teeth 42 during astart-up stage, a shut down stage, or an idle stage. Moreover, thegreater clearance exists while the system is not operating, such thatthe rotor 26 and stator housing 28 can be separated from one another forservicing, replacement, inspection, or other reasons.

A first stopper 46 is provided on the top side 44 of the packing ring 30to maintain a gas cavity between the packing ring 30 and the statorhousing 28 during start-up and shut down conditions of the machine. Aplurality of second stoppers 48 are provided on a bottom side 50 of thepacking ring 30 to limit the amount of engagement of the packing ring 30against the plurality of teeth 42. Thus, the stoppers 46 and 48 define arange of movement for the first seal portion or packing ring 30. In thismanner, the packing ring 30 can move radially inward and outwardrelative to the rotor 26, and specifically the plurality of teeth 42, toadjust the seal clearance during various stages of operation.

Referring to FIG. 4, a partial cross-sectional view of a bottom side ofthe abradable coating 34 facing the plurality of teeth is illustrated.In the illustrated embodiment, the abradable coating 34 includes aplurality of drilled holes 35 configured to control rotor dynamics. Inanother exemplary embodiment, the abradable coating 34 includes ahoneycomb structure configured to control the rotor dynamics. In otherexemplary embodiments, the coating may also include other structuresconfigured to control rotor dynamics response of the rotor. For example,the abradable structure or coating 34 may include a plurality of layersof different materials, different porosities/solidities, differenthardnesses, different wear properties, different thermal properties(e.g., coefficients of thermal expansion), different thicknesses,different frictional properties, or combinations thereof In one example,the abradable structure or coating 34 may include a plurality ofconcentric rings. The abradable coating in accordance with aspects ofthe present invention provides a high strength to weight ratio and astiffer, stable coating. The cavity of the drilled holes in thehoneycomb structure provide pneumatic damping to control rotor dynamics.

Referring to FIG. 5, a diagrammatical axial view of the sealing system24 is illustrated. In the illustrated embodiment, as discussedpreviously, the rotor 26 (located at the center) is disposed inside thestator housing 28. The I-shaped packing ring 30 is disposed in the slotformed in the stator housing 28. The packing ring 30 includes theabradable coating 34 provided on the substrate 36. The spring 38 isdisposed between the packing ring 30 and the stator housing 28. Thespring 38 is configured to bias the packing ring 30 away from pluralityof teeth 42 provided on the rotor 26. In the illustrated embodiment, theposition of only one of the plurality of springs 38 is illustrated forsimplicity. Although one packing ring 30 is illustrated in FIG. 4, thesystem may include multiple packing rings 30 disposed between the rotor26 and the stator housing 28. Similarly, multiple springs 38 may bedisposed between each packing ring 30 and the stator housing 28. Asmentioned previously, the first stopper 46 is provided on the top sideof the packing ring 30 to maintain a gas cavity between the packing ring30 and the stator housing 28 during start-up and shut down conditions ofthe machine. The second stopper 48 is provided on the bottom side of thepacking ring 30 to limit the amount of engagement of the packing ring 30against the plurality of teeth 42.

Referring to FIG. 6, another embodiment of the sealing system 24 isillustrated in accordance with aspects of the present invention. Asmentioned in previous embodiments, the sealing system 24 is disposedbetween the rotor 26 and the stator housing 28. The sealing system 24includes the packing ring 30 disposed in the slot 32 formed in thestator housing 28. In the illustrated embodiment, the second sealportion 40 includes a plurality of teeth 51 (e.g. “J” strip type)detachably fitted to a plurality of annular grooves, channels, or slots52 formed in the rotor 26. A plurality of wires 54 (e.g., ring-shapedwires) may be used to hold the plurality of teeth 51 in the slots 52formed in the rotor 26. The plurality of teeth 51 protrudes radiallyoutwards to the packing ring 30. As discussed in previous embodiments,the springs 38 are configured to bias the packing ring 30 away from tipportions of the plurality of teeth 51 fitted to the slots 52 formed inthe rotor 26. The illustrated example provides the additional advantagethat the plurality of teeth 51 may be replaced if the plurality of teeth51 are damaged or worn due to interference, due to the fact that theplurality of teeth 51 are detachably fitted to the rotor 26.

Referring to FIG. 7, another embodiment of the sealing system 24 isillustrated in accordance with aspects of the present invention. Thesealing system 24 is disposed between the rotor 26 and the statorhousing 28. The sealing system 24 includes the packing ring 30 disposedin the slot 32 formed in the stator housing 28. In this exemplaryembodiment, the plurality of teeth 42 are provided on the packing ring30 rather than the rotor 26, while the abradable structure or coating 34is provided on the rotor 26 rather than the ring 30. The plurality ofbiasing members 38, such as springs, are disposed between the packingring 30 and the stator housing 28. The springs 38, as mentionedpreviously, are configured to bias the packing ring 30 away from thesecond seal portion 40 provided on the rotor 26. In the illustratedembodiment, the second seal portion 40 includes the abradable coating 34provided on the rotor 26. During start-up and shut down of the machine,the springs 38 bias the packing ring 30 having the plurality of teeth 42away from the abradable coating 34 provided on the rotor 26. Duringoperation of the machine, the operating gas pressure pushes the packingring 30 against the abradable coating 34 provided on the rotor 26 tomaintain minimal clearance and reduce gas leakage. As discussedpreviously, during start up of the rotary compressor, the tip portionsof the plurality of teeth 42 slide over the surface of the abradablecoating 34 due to the interference between the packing ring 30 and theabradable coating 34. The combined effect of centrifugal forces and theforces resulting from biasing the packing ring 30 against the abradablecoating 34 dislodges the particles in the abradable coating 34, causingan incursion of the teeth 42 in the abradable coating 34.

In yet another embodiment similar to the embodiment illustrated in FIG.6, a plurality of teeth may be detachably fitted to slots formed in thepacking ring 30. The plurality of teeth protrudes downwards to a surfaceof the rotor 26. For example, the teeth may engage the rotor 26 at anannularly raised surface, an annularly recessed surface, or acombination thereof. Flow of fluid is throttled at locations where theteeth are provided on the packing ring 30. The raised and/or recessedsurface of the rotor 26 also functions to divert fluid flow along aradial direction providing a more tortuous path relative to the rotor26.

Referring to FIG. 8, this drawing illustrates an exemplary system, suchas a steam turbine 56, in accordance with certain embodiments of thepresent invention. The steam turbine 56 includes a rotating turbinebucket 58 disposed in a stationary turbine housing 60. A retractableabradable sealing system 62 is disposed between the rotating turbinebucket 58 and the stationary turbine housing 60. The sealing system 62includes a packing ring 64 disposed in a slot 66 provided in thestationary turbine housing 60. The packing ring 64 is also disposedadjacent to the turbine bucket 58, separating pressure regions onaxially opposite sides of the packing ring 64. The packing ring 64includes an abradable structure or coating 67 provided on a substrate68. The coating 67 is provided facing a plurality of radial projections70 and grooves 72 provided on the turbine bucket 58. The abradablecoating 67 is of a design for obtaining close clearances with the radialprojections and grooves provided on the turbine bucket 58. In certainembodiments, the abradable structure or coating 67 may have a geometryat least partially matched with the geometry of the projections 70 andgrooves 72. In other words, the abradable structure or coating 67 mayhave recesses corresponding to the projections 70 and extensionscorresponding to the grooves 72. In this manner, the abradable structureor coating 67 may provide a labyrinth type seal in addition to the wearproperties and clearance adjustment characteristics discussed in detailabove. These mating geometrical structures also may be withdrawn out ofengagement with one another during non-operational conditions, such thatthe turbine bucket 58 and the housing 60 can be separated from oneanother for servicing, maintenance, inspection, replacement, and soforth.

In the illustrated embodiment of FIG. 8, a retractable mechanism 74including a plurality of biasing members 76, such as springs, aredisposed between the packing ring 64 and the stationary turbine housing60. The springs 76 are configured to bias the packing ring 64 away fromthe projections 70 and grooves 72 provided on the turbine bucket 58. Thepacking ring 64 is radially movable with respect to the housing 60 asindicated by arrow 69. The abradable coating 67 generally protectspacking ring 64 against possible wear due to interference between thepacking ring 64, itself, and the plurality of projections 70 duringtypical operating conditions, such as during start-up, and transientconditions of the steam turbine 56.

During operation of the steam turbine, gas enters through the suctionports and exits through the discharge ports of the stationary turbinehousing 60. The gas pressure exerted on a top side of the packing ring64 forces the packing ring 64 against the plurality of projections 70provided on the turbine bucket 58 to maintain a minimal clearancebetween the packing ring 64 and the projections 70. In this manner, theminimized clearance improves operational efficiency and performance ofthe system.

During start-up, shut down, or other conditions in which gas pressure isminimum, the springs 76 bias the packing ring 64 away from theprojections 70 ensuring preservation of the projections 70. In otherwords, a greater clearance exists between the coating 67 and projections70 during a start-up stage, a shut down stage, or an idle stage.Moreover, the greater clearance exists while the system is notoperating, such that the rotating turbine bucket 58 and stationaryturbine housing 60 can be separated from one another for servicing,replacement, inspection, or other reasons.

A first stopper 78 is provided on the top side of the packing ring 64 tomaintain a gas cavity between the packing ring 64 and the stationaryturbine housing 60 during start-up and shut down conditions of the steamturbine 56. A plurality of second stoppers 80 are provided on a bottomside of the packing ring 64 to limit the amount of engagement of thepacking ring 64 against the plurality of projections 70. Thus, thestoppers 78 and 80 define a range of movement for the packing ring 64.In this manner, the packing ring 64 can move radially inward and outwardrelative to the rotating turbine bucket 58, and specifically theplurality of projections 70, to adjust the seal clearance during variousstages of operation.

Referring to FIG. 9, a flow chart illustrating exemplary steps involvedin method of operating a rotary machine (example, rotary compressor) isillustrated. In accordance with the illustrated exemplary embodiment,the method includes rotating the first member relative to the secondmember, or the second member relative to the first member as representedby step 82. In one example, the first member comprises the rotor and thesecond member comprises the stator housing. The sealing system isdisposed between the first member and the second member. The sealingsystem includes the first seal portion disposed in a groove, channel, orslot formed in the second member. For example, the first seal portionmay include the I-shaped packing ring, which can move radially inwardand outward relative to the second member. The packing ring includes theabradable structure disposed on the substrate.

During operation of the machine, gas enters through the suction portsand exits through the discharge ports of the second member. The gaspressure exerted on the top side of the first seal portion forces thefirst seal portion against the second seal portion (i.e. plurality ofteeth) provided on the first member to maintain a minimal clearancebetween the first seal portion and the second seal portion asrepresented by step 84. During start up of the rotary compressor, thetip portions of the plurality of teeth slide over the surface of theabradable coating due to the interference between the packing ring andthe teeth. The combined effect of centrifugal forces and the forcesresulting from biasing the packing ring against the teeth dislodges theparticles in the abradable coating, causing an incursion of the teeth inthe abradable coating. As a result, a plurality of permanent sealinggrooves may be formed in the abradable coating. The sealing grooves mayhave a profile matching as that of the teeth. As a result, closeclearance is maintained between the sealing elements.

During start-up, shut down, or other conditions in which gas pressure isminimum, the springs bias the first seal portion away from the secondseal portion ensuring preservation of the first seal portion and thesecond seal portion. The first stopper provided on the top side of thefirst seal portion facilitates to maintain a gas cavity between thefirst seal portion and the second member during start-up and shut downconditions of the machine. The plurality of second stoppers provided onthe bottom side of the first seal portion facilitates to limit theamount of engagement of the first seal portion against the second sealportion as represented by step 86. During operation of the machine, thefirst seal portion engages the second seal portion provided on the firstmember to provide a zero-clearance labyrinth seal between the firstmember and the second member as represented by step 88.

Referring to FIG. 10, a flow chart illustrating exemplary steps involvedin a method of manufacturing the rotary machine (example, rotarycompressor) is illustrated. In accordance with the illustrated exemplaryembodiment, the method includes disposing the retractable abradablesealing system between the first member and the second member configuredto control the leakage of fluid between the first member and the secondmember as represented by step 90. In one example, the first membercomprises the rotor and the second member comprises the stator housing.The sealing system 24 includes the first seal portion (e.g., I-shapedpacking ring), disposed in the slot formed in the stator housing. Thepacking ring includes the abradable structure (e.g. abradable coating)provided on the substrate.

The method includes disposing the retractable mechanism in the secondmember (packing ring) as represented by step 92. In the illustratedembodiment, the retractable mechanism including the plurality of biasingmembers, such as springs, are disposed between the first seal portionand the second seal portion as represented by step 94. The springs areconfigured to bias the first seal portion away from the second sealportion provided on the rotor. The first seal portion is radiallymovable with respect to the second member. The method further includesdisposing the second seal portion (one or more sealing teeth) on thefirst member in such a way so as to mate with the first seal portion toprovide a zero-clearance labyrinth seal during operation of the machineas represented by step 96.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A rotary machine, comprising: a first member; a second member,wherein the first member is configured to rotate relative to the secondmember or the second member is configured to rotate relative to thefirst member; and a retractable abradable seal disposed between thefirst and second members.
 2. The rotary machine of claim 1, wherein theretractable abradable seal configured to provide a generallyzero-clearance labyrinth seal between the first and second members. 3.The rotary machine of claim 1, wherein the retractable abradable sealcomprises an abradable structure coupled to a retractable mechanism. 4.The rotary machine of claim 3, wherein the retractable mechanism isrecessed at least partially into the second member.
 5. The rotarymachine of claim 1, wherein the retractable abradable seal comprises aretractable seal portion coupled to the second member and an abradableseal portion coupled to the first member opposite from the retractableseal portion.
 6. The rotary machine of claim 1, wherein the retractableabradable seal comprises an abradable seal portion disposed oppositefrom one or more sealing teeth.
 7. The rotary machine of claim 6,wherein the plurality of teeth are configured to form a plurality ofpermanent sealing grooves in the abradable seal portion.
 8. The rotarymachine of claim 7, wherein the plurality of teeth are configured toengage the plurality of permanent sealing grooves formed in theabradable seal portion during normal operation of the machine.
 9. Therotary machine of claim 1, wherein the rotary machine comprises aturbine, a compressor, a combustor, or a combination thereof.
 10. Therotary machine of claim 1, wherein the rotary machine comprises a steamturbine.
 11. A system, comprising: a retractable abradable seal,comprising: a retractable mechanism configured to couple to a secondmember opposite from a first member, wherein the first member or thesecond member is configured to rotate; a first seal portion disposed onthe retractable mechanism; and a second seal portion configured to bedisposed on the first member and mate with the first seal portion,wherein the first seal portion or the second seal portion comprises anabradable structure.
 12. The system of claim 11, wherein the retractableabradable seal is configured to provide a generally zero-clearancelabyrinth seal between the first and second members.
 13. The system ofclaim 11, wherein the first member comprises a rotary member.
 14. Thesystem of claim 11, wherein the second member comprises a stationarymember.
 15. The system of claim 11, wherein the abradable structurecomprises an abradable coating.
 16. The system of claim 11, wherein theabradable structure comprises cobalt, or, nickel, or, chromium, or,aluminum, or, yttrium, or, hexagonal boron nitride, or polymers, or acombination thereof.
 17. The system of claim 11, wherein the abradablestructure comprises nickel, or, chromium, or, aluminum, or clay, or acombination thereof.
 18. The system of claim 11, wherein the abradablestructure comprises nickel, or, graphite, or, stainless steel, or acombination thereof.
 19. The system of claim 11, wherein the abradablestructure comprises nickel, or, chromium, or, iron, or, aluminum, or,boron, or nitrogen, or a combination thereof.
 20. The system of claim11, wherein the abradable structure comprises a plurality of drilledholes configured to reduce vibration.
 21. The system of claim 11,wherein the retractable mechanism comprises one or more springsconfigured to bias the first seal portion away from the second sealportion.
 22. The system of claim 11, wherein the retractable mechanismcomprises one or more permanent magnets, or electromagnets configured tobias the first seal portion away from the second seal portion.
 23. Thesystem of claim 11, wherein the first seal portion comprises theabradable structure and the second seal portion comprises one or moresealing teeth, or the first seal portion comprises one or more sealingteeth and the second seal portion comprises the abradable structure, ora combination thereof.
 24. The system of claim 23, wherein the pluralityof sealing teeth are configured to form a plurality of permanent sealinggrooves in the abradable structure.
 25. The system of claim 24, whereinthe plurality of sealing teeth are configured to engage the plurality ofpermanent sealing grooves formed in the abradable structure duringnormal operation of the system.
 26. The system of claim 11, wherein theretractable mechanism is disposed at least partially in a gas chamber.27. The system of claim 11, wherein the retractable mechanism comprisesa first stopper and a second stopper opposite the first stopper, and thefirst and second stoppers are configured to limit a range clearancebetween the first and second seal portions.
 28. A method, comprising:rotating a first member relative to a second member or rotating thesecond member relative to the first member; and providing azero-clearance labyrinth seal between the first and the second membersvia a retractable abradable seal disposed between the first and thesecond members.
 29. The method of claim 28, wherein providing azero-clearance labyrinth seal comprises biasing a retractable sealportion coupled to the second member against an abradable seal portioncoupled to the first member.
 30. The method of claim 28, whereinproviding a zero-clearance labyrinth seal comprises biasing an abradableseal portion coupled to the second member against one or more sealingteeth coupled to the first member.
 31. The method of claim 30, whereinproviding a zero-clearance labyrinth seal comprises abrading a coatingformed in the abradable seal portion to form a plurality of permanentsealing grooves in the coating.
 32. The method of claim 30, furthercomprising biasing the abradable seal portion away from one or more sealteeth via one or more springs.
 33. The method of claim 30, whereinproviding a zero-clearance labyrinth seal comprises limiting a rangeclearance between the abradable seal portion and one or more sealingteeth via a first stopper and a second stopper.
 34. A method,comprising: disposing a retractable abradable seal between a firstmember and a second member, comprising coupling a retractable mechanismto the second member opposite from the first member, wherein the firstmember or the second member is configured to rotate; disposing a firstseal portion on the retractable mechanism; and disposing a second sealportion on the first member to mate with the first seal portion; whereinthe first seal portion or the second seal portion comprises an abradablestructure.
 35. The method of claim 34, wherein disposing the retractableseal between the first and second members comprises providing azero-clearance labyrinth seal between the first and second members. 36.The method of claim 34, comprising providing an abradable coating on thefirst seal portion or the second seal portion.
 37. The method of claim34, wherein coupling the retractable mechanism comprises providing oneor more springs configured to bias the first seal portion away from thesecond seal portion.
 38. The method of claim 37, comprising disposingthe retractable mechanism at least partially in a gas chamber.
 39. Themethod of claim 37, wherein disposing the retractable mechanismcomprises providing a first stopper and a second stopper opposite thefirst stopper and configured to limit a range clearance between thefirst and second members.